The present invention relates to catalytic gas detectors.
It is well known to use a pair of resistance thermometer sensors, one of which is coated with a suitable catalyst, for detecting the presence of a combustible or decomposible gas or gas mixture. Typically, current is passed through the thermometer sensors to heat them to a temperature at which the combustion or decomposition reaction of the gas or gas mixture to be detected can be catalysed by the catalytic coating. A typical temperature is 400.degree. C. If, for example, a combustible gas mixture is present, combustion occurs at the catalytic coating, raising the temperature of the coated sensor above that of the uncoated. This temperature difference is sensed by using a suitable electric circuit and can indicate the presence and concentration of the gas.
The composition of the catalytic coating is a matter of choice depending on the reaction which it is desired to catalyse. Numerous catalytic substances are known for both combustion and decomposition reactions. Thus, the term "catalytic coating" used hereinafter should be considered to include a coating of any catalytic substance useful in catalysing a gaseous combustion and/or decomposition reaction.